Open framework for the definition of metadata

ABSTRACT

A family of Java interfaces defines methods to provide common information about a property, such as data type and editing capabilities. The interfaces identify the methods used to get generic metadata. Implementers may extend these classes, as needed, to provide the metadata for their specific properties. The common metadata description interface of the present invention allows multiple metadata sources to be used interchangeably within the same software product without the software code being specifically written for each metadata source.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to data processing and, in particular, to the definition of metadata in the Java programming language. Still more particularly, the present invention provides an open framework for the definition of metadata.

2. Description of Related Art

Java is a programming language designed to generate applications that can run on all hardware platforms without modification. Java is an interpreted language. The source code of a Java program is compiled into an intermediate language called “bytecode,” which cannot run by itself. The bytecode must be converted (interpreted) into machine code at runtime. Upon finding a Java applet, e.g., in a Web page, a Web browser invokes a Java interpreter (Java Virtual Machine (JVM)) which translates the bytecode into machine code and runs it. JVMs are available for most hardware platforms. Thus, Java programs are not dependent on any specific hardware and will run in any computer with the Java Virtual Machine software. On the server side, Java programs can also be compiled into machine language for fastest performance, but they lose their hardware independence as a result.

JavaBeans are a component software architecture that runs in the Java environment. JavaBeans are independent Java program modules that are called for and executed. They have been used primarily for developing user interfaces at the client side. The server-side counterpart is Enterprise JavaBeans (EJBs). Java programs may also reference data sources other than JavaBeans and EJBs. For example, a Java program may reference a database made up of tables. Each source of data may have a different associated metadata. Metadata is data that describes other data. Data dictionaries and repositories are examples of metadata.

With different metadata sources, programmers must anticipate every possible metadata source and write code to communicate properly with each metadata source. If code is written for a plurality of metadata sources, the code may become very complicated. Furthermore, it is impossible to anticipate new metadata formats in the future. If an enterprise wishes to add a new data type and, thus, a new metadata source, the code must be completely rewritten. Therefore, it would be advantageous to provide an open framework for the definition of metadata.

SUMMARY OF THE INVENTION

The present invention provides a family of Java interfaces that define methods to provide common information about a property, such as data type and editing capabilities. The interfaces identify the methods used to get generic metadata. Implementers may extend these interfaces, as needed, to provide the metadata for their specific properties. For example, when a relational database is added, a programmer may write an object descriptor and a property descriptor classes that extend the interfaces. The common metadata description interface of the present invention allows multiple metadata sources to be used interchangeably within the same software product without the software code being specifically written for each metadata source.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

FIG. 1 depicts a pictorial representation of a network of data processing systems in which the present invention may be implemented;

FIG. 2 is a block diagram of a data processing system that may be implemented as a server in accordance with a preferred embodiment of the present invention;

FIG. 3 is a block diagram illustrating a data processing system in which the present invention may be implemented;

FIG. 4 is a block diagram illustrating the structure of the family of Java interfaces used to provide common information about generic properties in accordance with a preferred embodiment of the present invention;

FIG. 5 is a block diagram illustrating an implementation of the common interface in accordance with a preferred embodiment of the present invention;

FIG. 6 is an example of an implementation of the common interface in accordance with a preferred embodiment of the present invention; and

FIG. 7 is a flowchart illustrating the operation of an application implementing the common interface in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to the figures, FIG. 1 depicts a pictorial representation of a network of data processing systems in which the present invention may be implemented. Network data processing system 100 is a network of computers in which the present invention may be implemented. Network data processing system 100 contains a network 102, which is the medium used to provide communications links between various devices and computers connected together within network data processing system 100. Network 102 may include connections, such as wire, wireless communication links, or fiber optic cables.

In the depicted example, a server 104 is connected to network 102 along with storage unit 106. In addition, clients 108, 110, and 112 also are connected to network 102. These clients 108, 110, and 112 may be, for example, personal computers or network computers. In the depicted example, server 104 provides data, such as boot files, operating system images, and applications to clients 108-112. Clients 108, 110, and 112 are clients to server 104. Network data processing system 100 may include additional servers, clients, and other devices not shown. In the depicted example, network data processing system 100 is the Internet with network 102 representing a worldwide collection of networks and gateways that use the TCP/IP suite of protocols to communicate with one another. At the heart of the Internet is a backbone of high-speed data communication lines between major nodes or host computers, consisting of thousands of commercial, government, educational and other computer systems that route data and messages. Of course, network data processing system 100 also may be implemented as a number of different types of networks, such as for example, an intranet, a local area network (LAN), or a wide area network (WAN). FIG. 1 is intended as an example, and not as an architectural limitation for the present invention.

In accordance with a preferred embodiment of the present invention, Java programs may be called from within HTML documents or launched stand alone within network data processing system 100. When a Java program runs on a client, such as clients 108, 110, 112, it is often called a “Java applet.” When it is run on a server, such as server 104, it is called a “servlet.”

The present invention provides a family of Java interfaces that define methods to provide common information about a property, such as data type and editing capabilities. Implementers may extend these classes as needed to provide the metadata for their specific properties. For example, one embodiment of the present invention is an implementation that provides metadata descriptions of columns in a database table could be realized using Java DataBase Connectivity. Another example may be an implementation that uses Java introspection to glean metadata information about any bean object. The common metadata description interface of the present invention allows these two implementations to be used interchangeably within the same software product.

Referring to FIG. 2, a block diagram of a data processing system that may be implemented as a server, such as server 104 in FIG. 1, is depicted in accordance with a preferred embodiment of the present invention. Data processing system 200 may be a symmetric multiprocessor (SMP) system including a plurality of processors 202 and 204 connected to system bus 206. Alternatively, a single processor system may be employed. Also connected to system bus 206 is memory controller/cache 208, which provides an interface to local memory 209. I/O bus bridge 210 is connected to system bus 206 and provides an interface to I/O bus 212. Memory controller/cache 208 and I/O bus bridge 210 may be integrated as depicted.

Peripheral component interconnect (PCI) bus bridge 214 connected to I/O bus 212 provides an interface to PCI local bus 216. A number of modems may be connected to PCI bus 216. Typical PCI bus implementations will support four PCI expansion slots or add-in connectors. Communications links to network computers 108-112 in FIG. 1 may be provided through modem 218 and network adapter 220 connected to PCI local bus 216 through add-in boards.

Additional PCI bus bridges 222 and 224 provide interfaces for additional PCI buses 226 and 228, from which additional modems or network adapters may be supported. In this manner, data processing system 200 allows connections to multiple network computers. A memory-mapped graphics adapter 230 and hard disk 232 may also be connected to I/O bus 212 as depicted, either directly or indirectly.

Those of ordinary skill in the art will appreciate that the hardware depicted in FIG. 2 may vary. For example, other peripheral devices, such as optical disk drives and the like, also may be used in addition to or in place of the hardware depicted. The depicted example is not meant to imply architectural limitations with respect to the present invention.

The data processing system depicted in FIG. 2 may be, for example, an IBM e-Server pSeries system, a product of International Business Machines Corporation in Armonk, N.Y., running the Advanced Interactive Executive (AIX) operating system or LINUX operating system.

With reference now to FIG. 3, a block diagram illustrating a data processing system is depicted in which the present invention may be implemented. Data processing system 300 is an example of a client computer. Data processing system 300 employs a peripheral component interconnect (PCI) local bus architecture. Although the depicted example employs a PCI bus, other bus architectures such as Accelerated Graphics Port (AGP) and Industry Standard Architecture (ISA) may be used. Processor 302 and main memory 304 are connected to PCI local bus 306 through PCI bridge 308. PCI bridge 308 also may include an integrated memory controller and cache memory for processor 302. Additional connections to PCI local bus 306 may be made through direct component interconnection or through add-in boards. In the depicted example, local area network (LAN) adapter 310, SCSI host bus adapter 312, and expansion bus interface 314 are connected to PCI local bus 306 by direct component connection. In contrast, audio adapter 316, graphics adapter 318, and audio/video adapter 319 are connected to PCI local bus 306 by add-in boards inserted into expansion slots. Expansion bus interface 314 provides a connection for a keyboard and mouse adapter 320, modem 322, and additional memory 324. Small computer system interface (SCSI) host bus adapter 312 provides a connection for hard disk drive 326, tape drive 328, and CD-ROM drive 330. Typical PCI local bus implementations will support three or four PCI expansion slots or add-in connectors.

An operating system runs on processor 302 and is used to coordinate and provide control of various components within data processing system 300 in FIG. 3. The operating system may be a commercially available operating system, such as Windows 2000, which is available from Microsoft Corporation. An object oriented programming system such as Java may run in conjunction with the operating system and provide calls to the operating system from Java programs or applications executing on data processing system 300. “Java” is a trademark of Sun Microsystems, Inc. Instructions for the operating system, the object-oriented operating system, and applications or programs are located on storage devices, such as hard disk drive 326, and may be loaded into main memory 304 for execution by processor 302.

Those of ordinary skill in the art will appreciate that the hardware in FIG. 3 may vary depending on the implementation. Other internal hardware or peripheral devices, such as flash ROM (or equivalent nonvolatile memory) or optical disk drives and the like, may be used in addition to or in place of the hardware depicted in FIG. 3. Also, the processes of the present invention may be applied to a multiprocessor data processing system.

As another example, data processing system 300 may be a stand-alone system configured to be bootable without relying on some type of network communication interface, whether or not data processing system 300 comprises some type of network communication interface. As a further example, data processing system 300 may be a Personal Digital Assistant (PDA) device, which is configured with ROM and/or flash ROM in order to provide nonvolatile memory for storing operating system files and/or user-generated data.

The depicted example in FIG. 3 and above-described examples are not meant to imply architectural limitations. For example, data processing system 300 also may be a notebook computer or hand held computer. Data processing system 300 also may be a kiosk or a Web appliance.

With reference to FIG. 4, a block diagram illustrating the structure of the family of Java interfaces used to provide common information about generic properties is shown in accordance with a preferred embodiment of the present invention. The interface IMetaPropertyDescriptor 402 defines methods that describe a single property. For example, IMetaPropertyDescriptor may describe one column in a database and the methods defined by the interface may include getName( ), getValueClass( ), createDefaultValue( ), cloneValue( ), getPropertyEditor( ), canConvertValue( ), and convertValue( ).

The interface IMetaPropertySetDescriptor 404 describes a set of properties, such as a group of columns in a database. The IMetaObjectDescriptor interface 406 extends IMetaPropertySetDescriptor to collect multiple associated property descriptions into a single object description. Interface 404 is a subclass of interface 406. The arrow between interface 402 and 404 represents association. The arrow indicates that an object that implements interface 404 has a one-way association with objects that implement interface 402. Besides inheritance and association, relationships may include aggregation, using, instantiation, and meta-class. The “1 . . . *” indicates the cardinality of the association; a property set is associated with one or more properties. This is a one-to-many association. Other cardinalities may include one-to-one or many-to-many.

The methods of the IMetaProperty Descriptor are as follows:

-   -   String getName( )         -   Get the programmatic name that identifies this property             descriptor;     -   Class getValueClass( )         -   Get the class that represents this property's data type;     -   Object createDefaultValue( )         -   Create a default value of this property;     -   Object cloneValue(Object value)         -   Given a value of the type defined by this property             descriptor, clone the value and return a new value of the             same type;     -   boolean canConvertValue(Class valueClass)         -   Given a value's data type class, test if the class is             convertible to the data type class represented by this             property descriptor;     -   Object convertValue(Object value)         -   Given a value, convert it to a value matching the data type             class represented by this property descriptor;     -   PropertyEditor getPropertyEditor( )         -   Get the property editor needed to edit a value described by             this property descriptor. (For a description of property             editors see the SUN Java Bean specification, Java Platform             Second Edition, version 1.1 API).

The methods of the IMetaPropertySetDescriptor interface are as follows:

-   -   Int getPropertyDescriptor Count( )         -   Get the number of property descriptors contained by this set             descriptor;     -   IMetaPropertyDescriptor getPropertyDescriptor(int propertyIndex)         -   Given the index of a property contained within this set, get             the property's descriptor;     -   IMetaPropertyDescriptor getPropertyDescriptor(String         propertyName)         -   Given the name of a property contained within this set, get             the property's descriptor;     -   String getName( )         -   Get the programmatic name that identifies this set of             property descriptors.

The methods of the IMetaObjectDescriptor interface are as follows:

-   -   Object createDefaultObject( )         -   Create an object of the type defined by this object             descriptor with all of it's contained properties set to             their default values;     -   Object cloneObject(Object object)         -   Given an object represented by this descriptor, clone the             object and return a new object of the same type and same             contained property values;     -   Object getPropertyValue(int propertyIndex, Object object)         -   Given the index of a property contained within this set and             the containing object represented by this descriptor,             extract the property's value.     -   Object getPropertyValue(String propertyName, Object object)         -   Given the name of a property contained within this set and             the containing object represented by this descriptor,             extract the property's value;     -   void setPropertyValue(int propertyIndex, Object object, Object         newValue)         -   Given the index of a property contained within this set and             the containing object represented by this descriptor and the             new property value, set the property to the new value;     -   void setPropertyValue(String propertyName, Object object, Object         newValue)         -   Given the name of a property contained within this set and             the containing object represented by this descriptor and the             new property value, set the property to the new value;     -   void addPropertyChangeListener (PropertyChangeListener listener)         -   Given a listener of property change events, add it to this             object descriptor. (For a description of property change             listeners see the SUN Java Bean specification, Java Platform             Second Edition, version 1.1 API);     -   void addPropertyChangeListener(String propertyName,         PropertyChangeListener listener)         -   Given a listener of property-change events and the name of             the property, add it to this object descriptor;     -   void removePropertyChangeListener (PropertyChangeListener         listener)         -   Given a listener of property change events, remove it from             this object descriptor;     -   void removePropertyChangeListener(String propertyName,         PropertyChangeListener listener)         -   Given a listener of property change events and the name of             the property, remove it from this object descriptor;     -   void addVetoableChangeListener (VetoableChangeListener listener)         -   Given a listener of vetoable change events, add it to this             object descriptor. (For a description of vetoable change             listeners see the SUN Java Bean specification, Java Platform             Second Edition, version 1.1 API);     -   void addVetoableChangeListener(String propertyName,         VetoableChangeListener listener)         -   Given a listener of vetoable change events and the name of             the property, add it to this object descriptor;     -   void removeVetoableChangeListener (VetoableChangeListener         listener)         -   Given a listener of vetoable change events, remove it from             this object descriptor;     -   void removeVetoableChangeListener(String propertyName,         VetoableChangeListener listener)         -   Given a listener of vetoable change events and the name of             the property, remove it from this object descriptor.

With reference now to FIG. 5, a block diagram illustrating an implementation of the common interface is shown in accordance with a preferred embodiment of the present invention. The interface IMetaPropertyDescriptor 502 defines methods that describe a single property. The interface IMetaPropertySetDescriptor 504 describes a set of properties, such as a group of columns in a database. The IMetaObjectDescriptor interface 506 collects multiple associated property descriptions into a single object description.

An ObjectDescriptor class 510 that implements the interface IMetaObjectDescriptor is created. For example, if an enterprise uses a relational database, a programmer may create an ObjectDescriptor specifically for the relational database. The ObjectDescriptor includes the actual code for the methods identified in interface 506 and may glean information about an object. Next, a PropertyDescriptor class 508 that implements interface IMetaPropertyDescriptor 502 is created to expose information about each property in the object. In other words, the PropertyDescriptor class includes the actual code for the methods that are identified in the IMetaPropertyDescriptor interface. These methods may be called to return metadata for a property. For example, for a relational database, each property may be represented by a column and the PropertyDescriptor may be written to provide the actual code for the methods identified in interface 502.

Interfaces 502, 504, 506 are universal. ObjectDescriptor and PropertyDescriptor classes are specific to a metadata source. An enterprise may create an OjbectDescriptor and one or more PropertyDescriptors when a metadata source is added. ObjectDescriptor and PropertyDescriptor classes may also be shared between enterprises. In fact, a developer of a data source, such as a database, may write an ObjectDescriptor and appropriate PropertyDescriptors to ship with the product. Once this framework is in place, software may be written as if all the programmer knows is that there is an object that has properties. This simplifies the programming significantly when multiple metadata sources are being used. Furthermore, software written for this open framework may be used even after new data sources are added.

Turning to FIG. 6, an example of an implementation of the common interface is shown in accordance with a preferred embodiment of the present invention. The interface IMetaPropertyDescriptor 602 defines methods that describe a single property. The interface IMetaPropertySetDescriptor 604 describes a set of properties, such as a group of columns in a database. The IMetaObjectDescriptor interface 606 collects multiple associated property descriptions into a single object description.

A DBTableObjectDescriptor class 612 that implements the interface IMetaObjectDescriptor is created. The DBTableObjectDescriptor class may glean information about the appropriate database table using APIs that talk to the backend database and use the methods defined in interface IMetaObjectDescriptor 606 to expose that information. Next, a DBColumnPropertyDescriptor class 608 that implements the IMetaPropertyDescriptor interface 602 is created to expose information about each appropriate database table column (again using APIs that talk to the backend database) and use the methods defined in interface IMetaPropertyDescriptor 602 to expose that information.

Similarly, a JavaBeanObjectDescriptor class 614 that implements the interface IMetaObjectDescriptor is created. The JavaBeanObjectDescriptor class may glean information about the JavaBean using Java's built-in object introspection mechanism and use the methods defined in interface IMetaObjectDescriptor 606 to expose that information. Next, JavaBeanPropertyDescriptor class 610 that implements the IMetaPropertyDescriptor interface 602 is created to expose information about each property in the JavaBean using Java's built-in method introspection mechanism. Thus, the family of Java interfaces that make up the common interface may be implemented to expose information from multiple metadata sources, in this example one source being a relational database and the other being a Java Bean object.

An example Java program for a property sheet editor written using the open framework of the present invention follows: // This is an example of a property sheet editor that uses // Java interfaces for describing property metadata in a // generic way. 1000 public class Example { // This method loads a set of text field editor GUIs with // the values of properties contained within an object // whose metadata is described using the // “IMetaObjectDescriptor” interface. 1005 public void load(IMetaObjectDescriptor objDesc, Object  objValue) { // Loop through all the property descriptors contained // within the object descriptor. 1010 for (int i=0; i < objDesc.getPropertyDescriptorCount( );  i++) { // Get a property descriptor from the object // descriptor. 1015 IMetaPropertyDescriptor propDesc =  objDesc.getPropertyDescriptor(i); // Get the programmatic name of the property // descriptor. 1020 String propName = propDesc.getName( ); // Extract from the object's value the value of the // property named by the property descriptor. 1025 Object propValue =  objDesc.getPropertyValue(propName, objValue); // Get a property editor for the property's value // from the property descriptor. 1030 PropertyEditor propEditor =  propDesc.getPropertyEditor( ); // Set the property editor to the value of the // property.  propEditor.setValue(propValue); // Create a text field editor GUI for the property. JTextField textField = new JTextPield( ); // Set the text field editor GUI's display text to // the textual representation of the property's // value. (The “getAsText” method of the property // editor performs the conversion to textual // representation.) textField.setText(propEditor.getAsText( )); // Associate the programmatic name of the property // descriptor with the text field editor GUI and // store it in the lookup table so that it can be // accessed later. 1035 textEditors.put(propName, textField); } } // This method saves a set of property values contained // within text field editor GUIs to an object whose // metadata is described using the “IMetaObjectDescriptor” // interface. 1050 public void save(IMetaObjectDescriptor objDesc, Object  objValue) { // Loop through all the property descriptors contained // within the object descriptor. 1055 for (int i=0; i < objDesc.getPropertyDescriptorCount( );  i++) { // Get a property descriptor from the object // descriptor. 1060 IMetaPropertyDescriptor propDesc =  objDesc.getPropertyDescriptor(i); // Get the programmatic name of the property // descriptor. 1065 String propName = propDesc.getName( ); // Get a property editor for the property's value // from the property descriptor. PropertyEditor propEditor =  propDesc.getPropertyEditor( ); // Access the text field editor GUI for the // property descriptor from the lookup table using // the property's programmatic name. JTextField textField =  (JTextField)textEditors.get(propName); // Set the property editor to the textual // representation of the property's value from the // text field editor GUI. (The “setAsText” method // of the property editor performs the conversion // from textual representation.) 1070 propEditor.setAsText(textField.getText( )); // Get the new value of the property from the // property editor. 1075 Object propValue = propEditor.getValue( ); // Insert the new value of the property named by // the property descriptor into the object's value. 1080 objDesc.setPropertyValue(propName, objValue,  propValue); } } // Lookup table structure for storing text field GUIs used // to edit property values. private HashMap textEditors = new HashMap( ); } In the example program, line 1000 defines a class. Then, line 1005 defines a method called “load” that takes an ObjectDescriptor and an object as values. In the example shown in FIG. 6, the method may receive DBTableObjectDescriptor and the database as values or the method may receive JavaBeanObjectDescriptor and a JavaBean as values. The “load” method gets the names and values for the object and places them in a graphical user interface for editing.

Next, in line 1010, the program uses the methods in the framework to get the number of properties and loops through the properties. Line 1015 gets the property descriptor from the object descriptor. Line 1020 gets the property name and line 1025 gets the property value. Next, line 1030 gets a property editor from the property descriptor. (For a description of property editors see SUN Java Bean specification, Java Platform Second Edition, version 1.1 API.) This is used to populate a text field user interface widget with a textual representation of the property's value. In line 1035, this text field widget is associated with the property's name and is saved to a lookup table.

Thereafter, line 1050 defines a method called “save” that takes an ObjectDescriptor and an object as values. Next, in line 1055, the program uses the methods in the framework to get the number of properties and loops through the properties. Line 1060 gets the property descriptor from the object descriptor. Line 1065 gets the property name. Next, line 1070 extracts the textual representation of the edited property value from the text field widget that was previously saved to a lookup table and converts it to the property value object using the property editor. Line 1075 gets the property value object from the property editor. Thereafter, in line 1080, the property's new value is saved back into the containing object. This completes the editing process.

As can be seen in the above example, a program may be written without identifying an object type or a metadata source. The example property sheet program may be used for multiple data sources and may be reused in any environment taking advantage of the open framework of the present invention. While the example program is written in Java, other programming languages may be used, such as C++.

With reference now to FIG. 7, a flowchart is shown illustrating the operation of an application implementing the common interface in accordance with a preferred embodiment of the present invention. The process begins and creates an ObjectDescriptor class for an object that implements the interface IMetaObjectDescriptor (step 702). The process uses the methods in the interface to expose information for the object (step 704). Next, the process creates a PropertyDescriptor class for an object that implements the IMetaPropertyDescriptor interface (step 706) and uses the methods in the interface to expose information about each property in the object (step 708). Thereafter the process ends.

Thus, the present invention solves the disadvantages of the prior art by providing a family of Java interfaces that makes up a common interface for multiple metadata sources. Classes that implement these interfaces may extend these classes as needed to provide the metadata for their specific properties. Multiple implementations may be used interchangeably within an application because of the common metadata description provided by the interfaces. This technique is useful in cases in which properties are dynamically created at runtime and, therefore, cannot be described using a concrete bean object defined at compile time.

It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media, such as a floppy disk, a hard disk drive, a RAM, CD-ROMs, DVD-ROMs, and transmission-type media, such as digital and analog communications links, wired or wireless communications links using transmission forms, such as, for example, radio frequency and light wave transmissions. The computer readable media may take the form of coded formats that are decoded for actual use in a particular data processing system.

The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 

1-9. (canceled)
 10. A computer implemented method for providing metadata about a set of properties, comprising: creating a first object describing metadata for a plurality of data sources, wherein the first object maintains a related set of properties; and creating a set of second objects describing metadata for respective properties of the data sources; wherein metadata concerning a respective property is obtained by invoking a method in the first object to identify the respective property, and then invoking a method in a respective one of the second objects to dynamically obtain the metadata concerning the respective property.
 11. The method of claim 10, wherein the first object and the set of second objects comprise interface objects.
 12. The method of claim 10, wherein each object in the set of second objects defines methods that describe a single property of a data source.
 13. The method of claim 10, wherein the first object collects multiple associated property descriptions into a single description. 14-22. (canceled)
 23. An apparatus embodied in a computer useable medium for defining metadata about a related set of properties, comprising: a computer useable medium a first object on the computer useable medium describing metadata for a plurality of data sources, wherein the first object maintains a related set of properties for the plurality of data sources; and a set of second objects on the computer useable medium describing metadata for respective properties of the data sources that are maintained by the first object.
 24. The apparatus of claim 23, wherein the first object and the set of second objects comprise interface objects.
 25. The apparatus of claim 23, wherein each object in the set of second objects defines methods that describe a single property of a data source.
 26. The apparatus of claim 23, wherein the first object collects multiple associated property descriptions into a single description. 27-29. (canceled)
 30. A computer program product comprising: a computer usable medium having computer usable program code for providing metadata about a set of properties, said computer program product including: computer usable program code for creating a first object describing metadata for a plurality of data sources, wherein the first object maintains a related set of properties; and computer usable program code creating a set of second objects describing metadata for respective properties of the data sources, wherein metadata concerning a respective property is obtained by invoking a method in the first object to identify the respective property, and then invoking a method in a respective one of the second objects to dynamically obtain the metadata concerning the respective property.
 31. The computer program product of claim 30, wherein the first object and the set of second objects comprise interface objects.
 32. The computer program product of claim 30, wherein each object in the set of second objects defines methods that describe a single property of a data source.
 33. The computer program product of claim 30, wherein the first object collects multiple associated property descriptions into a single description. 